WO2021196687A1

WO2021196687A1 - Multi-component-based electric field probe and magnetic field probe calibration system and method

Info

Publication number: WO2021196687A1
Application number: PCT/CN2020/133072
Authority: WO
Inventors: 魏兴昌; 张力
Original assignee: 浙江大学
Priority date: 2020-04-03
Filing date: 2020-12-01
Publication date: 2021-10-07
Also published as: CN111398882B; CN111398882A; US20210318404A1

Abstract

A multi-component-based electric field probe and magnetic field probe calibration system and method. Said calibration system comprises a microstrip line calibration assembly, a clamp, a vector network analyzer and a data processing unit; two groups of microstrip lines contained in the microstrip line calibration assembly can be distributed on different wiring layers of the same PCB, and can also be distributed on an independent PCB; a first group of microstrip lines consists of single microstrip lines or differential lines under common-mode excitation, and is used for generating a main component Hy of a magnetic field, and the second group of microstrip lines consists of differential lines under differential-mode excitation, and is used for generating a main component Ex of an electric field. Said calibration system uses two groups of microstrip lines to respectively generate a horizontal magnetic field component and a horizontal electric field component to measure the coupling degree of an electromagnetic field probe to an external electric field and magnetic field; furthermore, a calculation formula of a calibration factor is proposed, so that the limitation that only the coupling degree of a probe to a field to be measured can be measured by using a single magnetic field component or a single electric field component currently is overcome, and the coupling degree of the electric field probe to a magnetic field not to be measured and the coupling degree of the magnetic field probe to an electric field not to be measured can be fully measured.

Description

Multi-component-based electric field probe and magnetic field probe calibration system and method

Technical field

The invention relates to the technical field of probe calibration and measurement, in particular to a multi-component-based electric field probe and magnetic field probe calibration system and method.

Background technique

Electric field probes and magnetic field probes are used to detect unknown electromagnetic interference sources or near-field radiation from antennas. In order to accurately and quantitatively analyze the amount of radiation, it is necessary to know the proportional coefficient between the output voltage of the electric field probe and the magnetic field probe and the electric field and magnetic field to be measured. This coefficient is defined as the probe factor (PF). The International Standards Organization IEC stipulates that a single standard microstrip line is used as the calibration component. First, the electromagnetic full-wave software is used to simulate the electric and magnetic fields above the calibration component, and then the probe is used to measure the calibration component at the same position. The calibration factor is defined as the magnetic field probe/ The ratio of the output voltage of the electric field probe to the simulated magnetic field value/electric field value.

When the standard microstrip line works, one port is excitation, and the other port is a 50 ohm matched load. It is considered that the field generated during its work is the field of standard transverse electromagnetic waves. When the magnetic field probe is calibrated, place the magnetic field probe above the center of the standard microstrip line, and the opening of the magnetic field probe is parallel to the current direction of the microstrip line. The coupling of the magnetic field has nothing to do with the electric field generated by the microstrip line. The current calibration method of single microstrip line, to calculate the calibration factor of a specific type of probe, often only considers the coupling between the probe and the main component of the field to be measured. For example, when calibrating a magnetic field probe, only the amplitude of the magnetic field to be measured in a certain direction is considered (Such as _Hy ) and the ratio of the output voltage of the magnetic field probe. In the same way, when calibrating the electric field probe, only consider the ratio of the amplitude of the electric field to be measured in a certain direction (such as E _c ) to the output of the electric field probe. In this way, only the coupling capability of the magnetic field probe to be measured can be known, or the treatment of the electric field probe The coupling ability of measuring electric field.

For a magnetic field probe, when it is working, it will also be coupled to the electric field in space, and the coupled space electric field will contribute part of the output of the magnetic field probe, which is equivalent to the environmental noise of the probe. The current calibration method ignores the coupling of the space electric field when calculating PF. In the same way, for electric field probes, the coupling of the spatial magnetic field or the environmental noise generated by the spatial magnetic field at the output of the probe are usually ignored, which affects the accuracy of the calibration. Therefore, it is necessary to provide a probe calibration method that takes into account the coupling of the magnetic field and the electric field, to improve the calibration accuracy of the electric field probe and the magnetic field probe, and to evaluate the probe's ability to suppress environmental noise.

Summary of the invention

In order to overcome the shortcomings of the prior art, the present invention provides a multi-component-based electric field probe and magnetic field probe calibration system and method, which can be applied to the calibration of electric field probes and magnetic field probes. For the magnetic field probe, the coupling of the magnetic field to the magnetic field probe and the coupling of the electric field to the magnetic field probe are separately expressed, so as to accurately obtain the coupling capability of the magnetic field probe to be measured and the degree of inhibition of the magnetic field probe to the non-measured electric field component; for the electric field probe , The coupling of the electric field to the electric field probe and the coupling of the magnetic field to the electric field probe are separately expressed, so as to accurately obtain the coupling ability of the electric field probe to the electric field to be measured and the suppression degree of the electric field probe to the non-measured magnetic field. The invention extracts the coupling coefficients of the external electric field and magnetic field components and the electric field probe and the magnetic field probe respectively, and obtains a more comprehensive and accurate calibration factor of the electric field probe and the magnetic field probe.

In order to achieve the above objectives, the present invention adopts the following technical solutions:

A multi-component-based electric field probe and magnetic field probe calibration system, including microstrip line calibration components, fixtures, vector network analyzers and data processing units;

The microstrip line calibration component includes a first group of microstrip lines and a second group of microstrip lines, the two groups of microstrip lines are distributed on different wiring layers of the same PCB board or distributed on an independent PCB board; One end of the first group of microstrip lines is connected with a first matching load, and the other end of the first group of microstrip lines is a first excitation port; one end of the second group of microstrip lines is connected with a second matching load, The other end of the two sets of microstrip lines is the second excitation port; the first set of microstrip lines and the second set of microstrip lines are perpendicular to each other, and the calibration point is 1mm directly above the vertical crossing point, which is fixedly installed on the The calibrated probe on the fixture is perpendicular to the PCB board and the detection center of the calibrated probe coincides with the calibration point;

The vector network analyzer is respectively connected to the first excitation port on the first group of microstrip lines, the second excitation port on the second group of microstrip lines, and the output port of the probe to be schooled; The data processing unit is used to calculate the calibration factor of the calibrated field probe at each calibration frequency point.

As a preference of the present invention, the first group of microstrip lines adopts a single microstrip line or a differential line under common mode excitation to generate the magnetic field component _Hy ; the second group of microstrip lines adopts a differential line under differential mode excitation. The differential line is used to generate the electric field component E _x .

As a preference of the present invention, the calculation formulas of the calibration factors α and β are:

Among them, for magnetic field probes, α is the calibration factor of the probe to be measured magnetic field, β is the coupling degree of the probe to the non-measured electric field; for electric field probes, α is the coupling degree of the probe to the non-measured magnetic field, and β is the probe's electric field to be measured. Calibration factor;

Respectively indicate the magnetic field strength and electric field strength of the calibration point when 1W excitation power is applied to the first excitation port;

with

Respectively represent the magnetic field strength and electric field strength of the calibration point when 1W excitation power is applied to the second excitation port; S ₁₃ and S ₂₃ are the scattering parameters measured by the vector network analyzer; Z ₃ is the impedance of the probe terminal connection (usually 50 ohms).

The invention also discloses a calibration method based on the above-mentioned electric field probe and magnetic field probe calibration system, the steps are as follows:

1) Fix the relative position of the microstrip line calibration component and the field probe to be calibrated so that the field probe to be calibrated is perpendicular to the PCB board where the microstrip line is located, and the detection center of the field probe to be calibrated coincides with the calibration point;

2) Connect the first excitation port on the first group of microstrip lines, the second excitation port on the second group of microstrip lines, and the output port of the field probe to the vector network analyzer; The signal source inside the analyzer applies excitation signals of different calibration frequencies. For each calibration frequency f, the vector network analyzer measures the three-port scattering parameter matrix

Where S _ij (i,j=1, 2, 3) varies with frequency f;

3) For the microstrip line calibration component prepared according to step 1), apply 1W excitation power at the first excitation port on the first set of microstrip lines to obtain the magnetic field strength of the calibration point

And electric field strength

Similarly, apply 1W excitation power at the second excitation port on the second set of microstrip lines to obtain the magnetic field strength at the calibration point

And electric field strength

Bundle

As the reference value of the electromagnetic field generated by the microstrip calibration component;

_{4) According to the S 13} and S ₂₃ measured by the vector network analyzer in step 2) and the value obtained in step 3)

Use the following formula to calculate the calibration factors α and β of the field probe to be measured at each calibration frequency point:

Among them, for the magnetic field probe, α is the calibration factor of the probe to be measured, and β is the coupling degree of the probe to the non-measured electric field; for the electric field probe, α is the coupling degree of the probe to the non-measured magnetic field, and β is the probe's electric field to be measured. The calibration factor.

The beneficial effects of the present invention are:

The calibration system of the present invention uses two sets of microstrip lines, which can generate a main magnetic field component and a main electric field component perpendicular to each other in the horizontal plane; use the magnetic field and the electric field component to test the response of the electric field probe and the magnetic field probe to calibrate the probe, Two coupling coefficients are obtained.

In the probe calibration process, for the magnetic field probe, not only the coupling of the external magnetic field to the magnetic field probe is considered, but also the coupling of the external electric field to the magnetic field probe is further calculated, so that the coupling capability (or sensitivity of the magnetic field probe) of the magnetic field probe to be measured can be comprehensively and accurately measured. ) And the ability to suppress the electric field that is not under test. In the same way, for the electric field probe, not only the coupling of the external electric field to the electric field probe is considered, but also the coupling of the external magnetic field to the electric field probe is further calculated, so that the coupling capability (or sensitivity) of the electric field probe to be measured can be comprehensively and accurately measured. The ability to suppress the magnetic field to be measured. This method makes up for the limitation that the current single magnetic field component or single electric field component can only measure the coupling degree of the field to be measured by the probe, and can comprehensively measure the suppression degree of the electric field probe to the non-measured magnetic field and the magnetic field probe to the non-measured electric field. There is great reference value in electromagnetic near-field scanning.

Description of the drawings

Figure 1 is a schematic diagram of the calibration system of the present invention;

2 is a schematic diagram of a microstrip line calibration assembly in an embodiment of the present invention, in which two sets of microstrip lines are distributed on the same PCB board, are located on different wiring layers of the PCB and are perpendicular to each other;

Figure 3 (a) is a schematic diagram of the first set of microstrip line calibration in an embodiment of the present invention;

Figure 3(b) is a schematic diagram of the second set of microstrip line calibration in an embodiment of the present invention;

Fig. 4 is a comparison between the coupling coefficient of the present invention and the existing magnetic field calibration coefficient.

Detailed ways

The present invention will be further explained below in conjunction with the accompanying drawings of the specification.

A calibration system for electric and magnetic field probes based on multi-components. The calibration diagram is shown in Figure 1. It includes a microstrip calibration component, a fixture, a vector network analyzer, and a data processing unit. The calibration factor of the calibrated field probe at the calibration frequency point.

The microstrip line calibration component includes a first set of microstrip lines and a second set of microstrip lines. The two sets of microstrip lines can be distributed on different wiring layers of the same PCB board, as shown in Figure 2, or on a separate PCB board, as shown in Figure 3. The first group of microstrip lines is a single microstrip line. The strip line or the differential line under common mode excitation is used to generate the magnetic field component _Hy , the second group of microstrip lines are the differential line under the differential mode excitation, used to generate the electric field component E _x ; the first group of microstrip lines One end of the line is connected to the first matching load, and the other end of the first group of microstrip lines is the first excitation port; one end of the second group of microstrip lines is connected to the second matching load, and the second group of microstrip lines is The other end is the second excitation port; the first group of microstrip lines and the second group of microstrip lines are distributed/placed perpendicular to each other, and the calibration point is 1mm directly above the vertical intersection point, which is fixedly installed on the calibrated field on the fixture The probe is perpendicular to the PCB board and the detection center of the calibrated field probe coincides with the calibration point.

In the specific implementation of the present invention, the microstrip line calibration component is shown in Figure 2 (two sets of microstrip lines are on different wiring layers of the same PCB board) or Figure 3 (two sets of microstrip lines are on different PCB boards) .

1) The first group of microstrip lines: single, matched microstrip lines (as shown in Figure 1) or common mode excitation and matched differential lines (as shown in Figures 2 and 3), distributed along the x direction, and The main magnetic field component generated above is _Hy . One end of the microstrip line is connected to a matched load, and the other end is defined as excitation port 1 (for a single microstrip line, add excitation between the microstrip line and the ground plane; for a differential line, add an excitation between the two wires in parallel and the ground plane excitation).

2) The second group of microstrip lines: the other group is differential mode excitation and matching differential lines, distributed along the y direction. Using differential mode excitation (adding excitation between two wires), the main electric field component generated above it is E _x . One end of the differential microstrip line is connected to a matched load, and the other end is defined as the excitation port 2.

The calibration point is defined as 1mm directly above the intersection of the center lines of the two sets of microstrip lines. According to 1) -2) is disposed at the calibration point can be within the electromagnetic field components in two mutually perpendicular horizontal plane: E _x and H _y.

For the calibration components shown in Figure 2 where the two sets of microstrip lines are distributed on the same PCB board, the calibration probe is placed above the microstrip line through the fixture during calibration, and only needs to be measured once with a vector network analyzer; for the calibration components shown in Figure 3 Two sets of microstrip line calibration components are distributed on different PCB boards. During calibration, the field probes are placed above the two sets of microstrip lines. Keep the probe position unchanged. Replace the microstrip line and measure twice with a vector network analyzer. The detection center of the probe coincides with the calibration point, as shown in Figure 1, Figure 2, and Figure 3. The output terminal of the probe is defined as port 3.

For the structures shown in Figure 1, Figure 2, and Figure 3, the vector network analyzer is connected to port 1, port 2, and the output port 3 of the field probe to be calibrated, and the internal signal source of the vector network analyzer outputs excitations of different calibration frequencies. Signal. For each calibration frequency f, the S-parameter scattering matrix of the 3-port network is measured by a vector network analyzer, and the following model is established:

Where a ₁ to a ₃ and b ₁ to b ₃ are the incident waves and reflected waves at the three ports, respectively. The matrix element S _ij (i,j=1, 2, 3) changes with the frequency f and is measured by a vector network analyzer to meet the reciprocity.

Since the two sets of microstrip lines are well matched, the S scattering parameter theory and formula (1) can be obtained:

When 1V excitation voltage is applied to port 1 and port 2 is matched

When 1V excitation voltage is applied to port 2 and port 1 matches

In formulas (2) and (3), V ₃ is the voltage when port 3 is connected to impedance Z ₃ _{, and Z 1} and Z ₂ are the reference impedances of ports 1 and 2, respectively. Next, use the calibration algorithm to calculate the output voltage V _{3 of the} _{probe with the E x} and H _{y of the} calibration point, and make it equal to formulas (2) and (3) respectively, so as to solve the coupling coefficient of the probe to the external electric field and magnetic field.

1. Calibration Algorithm

Draw the microstrip line calibration component model, and use electromagnetic full-wave software to simulate, you can get E _x and H _y at the calibration point. The simulated microstrip line calibration component model must be consistent with the microstrip line used in the measurement, but does not include the probe and fixture parts. For the configuration shown in FIG. 1, the port voltage of 3 V ₃ by the electromagnetic field and the calibration points E _x H _y induced, and V ₃ and H _y E _x and to the following proportional relation:

V ₃ =αH _y +βE _x (4)

Among them, for the magnetic field probe, α is the calibration factor of the probe to be measured, and β is the coupling degree of the probe to the non-measured electric field; for the electric field probe, α is the coupling degree of the probe to the non-measured magnetic field, and β is the probe's electric field to be measured. The calibration factor. In formula (4), both the main horizontal electric and magnetic field components generated by the microstrip line calibration component are considered, as well as the secondary horizontal electric and magnetic field components.

When 1W excitation power is applied to port 1 and port 2 is matched, the electromagnetic field at the calibration point is obtained by simulation as

Converted to when 1V excitation voltage is applied to port 1 and combined with formula (4), we get

When 1W excitation power is applied to port 2 and port 1 is matched, the electromagnetic field at the calibration point is obtained by simulation as

Converted to when 1V excitation voltage is applied to port 2 and combined with formula (4), we get

Let (2)=(5), (3)=(6), get

(7) Formula is the calculation formula of the coupling coefficient finally obtained. in,

Measured by vector network analyzer,

Obtained from the simulation value of electromagnetic full-wave software, α and β are the calculated calibration factors or coupling coefficients.

Both α and β vary with frequency.

2. How to use the calibration factor

When the calibrated magnetic field probe is used to measure the magnetic field to be measured, take the test _Hy as an example, and the magnetic field probe is connected to a spectrum analyzer. According to the voltage V ₃ measured by the spectrum analyzer, the magnetic field to be measured can be calculated as _Hy = V ₃ /α; β It is used to measure the coupling degree of the magnetic field probe to the non-measured electric field. The smaller the β, the smaller the influence of the non-measured electric field on the magnetic field probe.

When the calibrated electric field probe is used to measure the electric field to be measured, take the test E _x as an example, and the electric field probe is connected to a spectrum analyzer. According to the voltage V ₃ measured by the spectrum analyzer, the electric field to be measured E _x =V ₃ /β can be calculated; α is used To measure the coupling degree of the electric field probe to the non-measured magnetic field, the smaller the α, the smaller the influence of the non-measured magnetic field on the electric field probe.

3. Calculation example of calibration factor

Fig. 4 is a calculation result of the calibration factor of a magnetic field probe _{for measuring a magnetic field Hy} by the present invention when the calibration microstrip line shown in Fig. 3 is used. Among them, "existing magnetic field calibration coefficient 1" refers to the magnetic field coupling factor obtained by the existing calibration method when the first group of microstrip lines in Figure 3(a) is used as the calibration component; "existing magnetic field calibration coefficient 2" refers to When the second set of microstrip lines in Fig. 3(b) are used as calibration parts, the magnetic field coupling factor obtained by the existing calibration method. The main difference between the existing calibration method and the calibration method of the present invention is that the existing calibration method only uses a set of microstrip lines as calibration components. It can be seen from the figure:

1) Fig. 3(a) The first set of differential lines excited by the common mode, the generated magnetic field _{Hy is} relatively large, and the electric field E _{x is} relatively small. At this time, the non-measured electric field E _x has a small influence on the magnetic field probe. Therefore, the magnetic field coupling coefficient α calculated by the present invention is in good agreement with the "existing magnetic field calibration coefficient 1", which proves that the present invention is compatible with the existing magnetic field calibration coefficient.

2) Fig. 3(b) The second group of differential lines excited by the differential mode, the generated magnetic field _{Hy is} small, and the electric field E _{x is} large. At this time, the non-measured electric field E _x has a greater impact on the magnetic field probe, so the "existing magnetic field calibration coefficient 2" has an error and deviates from the "existing magnetic field calibration coefficient 1". The magnetic field coupling coefficient α calculated by the present invention is in good agreement with the "existing magnetic field calibration coefficient 1", and the electric field coupling coefficient β calculated by the present invention can well explain the "existing magnetic field calibration coefficient 2" and the "existing magnetic field calibration coefficient 1". 1" The reason for the deviation: It is _{the coupling of the non-measured electric field E x} and the magnetic field probe (indicated by the coupling coefficient β) that makes the magnetic field probe produce errors when detecting weak magnetic fields.

The above-mentioned embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person of ordinary skill in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by equivalent substitutions or equivalent transformations fall within the protection scope of the present invention.

Claims

A multi-component-based calibration system for electric and magnetic field probes, which is characterized in that it includes a microstrip line calibration component, a fixture, a vector network analyzer, and a data processing unit;

The microstrip line calibration component includes a first group of microstrip lines and a second group of microstrip lines, the two groups of microstrip lines are distributed on different wiring layers of the same PCB board or distributed on an independent PCB board; One end of the first group of microstrip lines is connected with a first matching load, and the other end of the first group of microstrip lines is a first excitation port; one end of the second group of microstrip lines is connected with a second matching load, The other end of the two sets of microstrip lines is the second excitation port; the first set of microstrip lines and the second set of microstrip lines are perpendicular to each other, and the calibration point is 1mm directly above the vertical crossing point, which is fixedly installed on the The calibrated probe on the fixture is perpendicular to the PCB board and the detection center of the calibrated probe coincides with the calibration point;

The vector network analyzer is respectively connected to the first excitation port on the first group of microstrip lines, the second excitation port on the second group of microstrip lines, and the output port of the probe to be schooled; The data processing unit is used to calculate the calibration factor of the calibrated field probe at each calibration frequency point.
The multi-component-based electric field probe and magnetic field probe calibration system according to claim 1, wherein the first group of microstrip lines adopts a single microstrip line or a differential line under common mode excitation, and The two sets of microstrip lines use differential lines under differential mode excitation.
The multi-component-based electric field probe and magnetic field probe calibration system according to claim 1, wherein the calculation formula of the calibration factor is:

Among them, for the magnetic field probe, α is the calibration factor of the probe to be measured, and β is the coupling degree of the probe to the non-measured electric field; for the electric field probe, α is the coupling degree of the probe to the non-measured magnetic field, and β is the probe's electric field to be measured. Calibration factor;
Respectively indicate the magnetic field strength and electric field strength of the calibration point when 1W excitation power is applied to the first excitation port;
with
Respectively represent the magnetic field strength and electric field strength of the calibration point when 1W excitation power is applied to the second excitation port; S 13 and S 23 are the scattering parameters measured by the vector network analyzer; Z 3 is the impedance of the probe terminal connection; f is Calibration frequency.
A calibration method based on the electric field probe and magnetic field probe calibration system according to claim 1, characterized in that the steps are as follows:

1) Fix the relative position of the calibration component of the microstrip line and the probe to be calibrated so that the probe to be calibrated is perpendicular to the PCB board where the microstrip line is located, and the detection center of the probe to be calibrated coincides with the calibration point;

2) Connect the first excitation port on the first group of microstrip lines, the second excitation port on the second group of microstrip lines, and the output port of the field probe to the vector network analyzer; The signal source inside the analyzer applies excitation signals of different calibration frequencies. For each calibration frequency f, the vector network analyzer measures the three-port scattering parameter matrix
Where S ij (i,j=1, 2, 3) varies with frequency f;

3) For the microstrip line calibration component prepared according to step 1), apply 1W excitation power at the first excitation port on the first set of microstrip lines to obtain the magnetic field strength of the calibration point
And electric field strength
Similarly, apply 1W excitation power at the second excitation port on the second set of microstrip lines to obtain the magnetic field strength at the calibration point
And electric field strength
Bundle
As the reference value of the electromagnetic field generated by the microstrip calibration component;

4) According to the S 13 and S 23 measured by the vector network analyzer in step 2) and the value obtained in step 3)
Use the following formula to calculate the calibration factors α and β of the field probe to be measured at each calibration frequency point:

Among them, for the magnetic field probe, α is the calibration factor of the probe to be measured, and β is the coupling degree of the probe to the non-measured electric field; for the electric field probe, α is the coupling degree of the probe to the non-measured magnetic field, and β is the probe's electric field to be measured. The calibration factor.